The topographical distribution of TSSA and H-2 antigens of malignant line Ib lymphocytes will be analyzed by immunoelectron microscopy employing a double staining technique. Concomitantly, immune precipitates formed between radiolabeled, solubilized Ib antigen and either anti-TSSA or anti-H-2 will be analyzed by SDS-PAGE. The major emphasis of this investigation is the elucidation of any intimate association between the two cell surface antigens; i.e., whether they exist as a single protein moiety or two separate moieties. Experimentally, this will be done by electron microscopic observation of the redistribution, or lack, thereof, of the TSSA following capping of the H-2 antigen, Additionally, migration patterns of immune precipitates following SDS-PAGE will be analyzed for evidence of co-migration of the respective protein moieties.